The present invention relates generally to lift mechanisms and, more particularly, to lift mechanisms of the vertical travel type which are adapted to be used in raising and lowering a dentist's chair seat.
The practice of dentistry has progressed significantly over the years and, as a consequence, so have the requirements for modern dental equipment. In particular, more and more dentists have adopted a sitting as opposed to standing position in performing dentistry procedures. Consequently, a modern dental chair must be capable of being lowered to almost a floor level position to enable a sitting dentist to practice upon a patient who prefers to sit erect while, at the same time, be capable of elevating the chair to height sufficient to enable a standing dentist to practice. Thus, the range of elevations for a dental chair is fairly significant, e.g., from about 6 inches to about three feet or more.
Conventional lift mechanisms for dental chairs generally have a very limited range of elevation since if they are extended to above about a foot or more, the mechanism may tend to become quite unstable. For example, lift mechanisms utilizing telescoping members (see for example U.S. Pat. No. 657,360 to Ritter) tend to become unstable after the telescoping member has been extended by half its length or more since the combined strength of the members tends to decrease upon telescoping. In a like manner, lift mechanisms using a scissors-type jack (see, for example, U.S. Pat. No. 3,472,488 to Naughton) become more and more unstable as the jack is extended.
In addition, conventional lift mechanisms for dental chairs are generally located beneath the center portion of the chair seat. For a dentist who wishes to practice in the sitting position, the lift mechanism can present an obstacle for the comfortable positioning of his feet and legs and can limit access to a patient to a relatively few angles. This central positioning of the lift mechanism also physically limits the length of its extensible members for the lift mechanism and therefore limits the upward elevation range for the chair. The bulk of the cental positioned lift mechanism also limits the downward movement of the chair to a relatively high position and thereby may effectively prevent a setting dentist from working on a tall patient who wishes to sit in an erect position.
Conventional lift mechanisms also sometimes do not lift the chair seat totally in a vertical direction but rather lift with some forward or backward movement as well as with a vertical component. As a result a dentist using such a mechanism in a dental chair would have to change positions when adjusting the elevation of the chair seat in order to remain in the same horizontal position relative to the patient.
Advances in the field of dentistry have also made it necessary that the dentist have a wide array of dental accessories such as drills, stands, hoses, tools and the like at his immediate disposal when tending to a patient. Consequently, such dental accessories should preferably be carried by the chair itself so that, as the chair is raised or lowered to accommmodate the position of the dentist relative to a patient, the dental accessories will always be within easy reach. Conventional lift mechanisms for dental chairs have generally been unable to carry this additional weight due to the inherent instability of the mechanism as the chair seat is elevated, particularly at the higher elevations of the seat.
In view of the various deficiencies in conventional lift mechanisms for dental chairs, it would be desirable to provide a lift mechanism which, among other things, is stable at all positions, particularly at elevated positions, gives essentially unlimited access to the underside of the chair seat, enables dental accessories to be carried by the dental chair, can be lowered to a relatively low position relative to a floor, and enables a stable, smooth and essentially vertical travel of the chair seat with a minimum of noise and vibration.